Control of Spin-Wave Damping in YIG Using Spin Currents from Topological Insulators

Aryan Navabi, Yuxiang Liu, Pramey Upadhyaya, Koichi Murata, Farbod Ebrahimi, Guoqiang Yu, Bo Ma, Yiheng Rao, Mohsen Yazdani, Mohammad Montazeri, Lei Pan, Ilya N. Krivorotov, Igor Barsukov, Qinghui Yang, Pedram Khalili Amiri, Yaroslav Tserkovnyak, and Kang L. Wang

Phys. Rev. Applied 11, 034046 – Published 19 March 2019

Abstract

Spin waves in insulating materials such as Yttrium Iron Garnet (YIG) can be used for signal propagation and processing using the spin of the electrons rather than transport of their charge. Planar YIG films can be integrated with silicon technology to realize devices such as tunable filters, frequency selective limiters, and signal-to-noise enhancers. However, such films suffer from spin-wave damping, which limits their use in such applications. Here, we show that spin currents in topological insulators (TI) can be used to reduce spin-wave damping. TI supports surface spin currents, potentially making it an efficient source of antidamping torque. We show that in a YIG/ ${Bi}_{2} {Se}_{3}$ bilayer, the spin-wave damping rate can be reduced by 60% at a current density of $8 \times 10^{5} A/c m^{2}$ . Furthermore, we show that the damping reduction has a strong dependence on spin-wave frequency and we demonstrate that this dependence arises from nonlinear magnon scattering.

Received 3 September 2018
Revised 3 February 2019

DOI:https://doi.org/10.1103/PhysRevApplied.11.034046

Physics Subject Headings (PhySH)

Magnons Spin current Spin dynamics Spin torque Spin waves Spin-orbit coupling

Multilayer thin films Topological insulators

Condensed Matter, Materials & Applied Physics

Authors & Affiliations

Aryan Navabi^1,*, Yuxiang Liu¹, Pramey Upadhyaya², Koichi Murata¹, Farbod Ebrahimi³, Guoqiang Yu¹, Bo Ma⁴, Yiheng Rao⁴, Mohsen Yazdani¹, Mohammad Montazeri¹, Lei Pan¹, Ilya N. Krivorotov⁵, Igor Barsukov⁶, Qinghui Yang⁴, Pedram Khalili Amiri¹, Yaroslav Tserkovnyak², and Kang L. Wang¹

¹Department of Electrical Engineering, University of California, Los Angeles, California 90095, USA
²Department of Physics and Astronomy, University of California, Los Angeles, California 90095, USA
³Inston Inc., Los Angeles, California 90095, USA
⁴State Key Laboratory of Electronic Thin Films and Integrated Devices, University of Electronic Science and Technology of China, Chengdu 610054, China
⁵School of Physics and Astronomy, University of California, Irvine, California 92697, USA
⁶Department of Physics and Astronomy, University of California, Riverside, California 92521, USA

^*aryan.n@ieee.org

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Vol. 11, Iss. 3 — March 2019

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Images

Figure 1
Amplification of spin waves. (a) Optical image of the spin-wave device. (b) S parameters of the spin-wave device measured using a VNA. (c) A SG launches a spin wave while a current pulse drives a spin-polarized current in the TI that enhances the spin-wave signal. (d) The spin currents from TI (with spin polarization $\hat{σ}$ ) transfer angular momentum to the spin wave with wavenumber k. Damping is compensated at a critical current density, $J_{C}$ . (e) Spin-wave amplitude is controlled by spin currents from TI measured at 500 Oe and 3.39 GHz. The data is fitted (red solid line) using Eq. (2) (Inset: amplitude of the spin wave before and after the current pulse is applied).
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Figure 2
Dependence of the gain on spin-wave frequency. (a) Spin-wave amplitude measured using an oscilloscope/spectrum analyzer with the external magnetic field set to 500 Oe. (b) Different spin-wave frequencies show different amounts of gain. The markers show experimental data and the solid lines are the fits to Eq. (2). (c) The dependence of total gain on spin-wave frequency is illustrated by plotting the maximum total gain in dB. The figure shows that the gain is more significant for a narrow range of frequencies above the maximum transmission frequency. (d) The gain due to SOT vs the spin-wave pass band.
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Figure 3
Dependence of the gain enhancement on an external magnetic field. Spin-wave pass band spectrum (black circles) and total gain of spin-wave amplitude in dB (red triangles) with a current density of $8 \times 10^{5} A/c m^{2}$ at 450 Oe (a), 500 Oe (b), 550 Oe (c), and 900 Oe (d). The data shown in (b) is the same as that in Figs. 2 and 2 (red upward triangles) for comparison. The total gain has a peak at some frequency above the maximum transmission frequency (a–c), whereas the total gain in (d) does not show any enhancement for frequencies 400 MHz above the maximum transmission frequency.
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Figure 4
Three-magnon scattering in YIG. (a) Experimental data showing the S₂₁ parameter for 500 Oe. The white dashed line is a spin wave with a wavenumber that crosses $F_{th} \approx 3.38 GHz$ . The four black arrows highlight a line that separates the linear and nonlinear regions. For the spin wave with wavenumber corresponding to the white dashed line, beyond the magnetic field $H_{th}$ (solid black square), three-magnon scattering is suppressed and spin-wave transmission increases. (b) The dispersion curves for spin waves propagating at angles ranging from 0° to 90° with respect to H. The inset shows the scenario when a spin wave propagating at 90° (green rectangle) scatters to two other spin waves (blue circle).
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Figure 5
The change in spin-wave damping rate, $Δ η$ (orange squares) and critical current density, $J_{C}$ (black circles), for different external magnetic fields. At 450 Oe, the control of spin-wave damping rate is the most efficient where at $8 \times 10^{5} A/c m^{2}$ 60% of the damping rate is reduced. This is also shown in the critical current density data where the value of $J_{C}$ is lowest at 450 Oe. The gray hexagonal markers are the critical current densities when group velocities are recalculated by taking the effect of the metal lines on the dispersion relationship into account. This increases $J_{C}$ at 450 Oe to $1.5 \times 10^{6} A/c m^{2}$ .
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